The effects of aging on functional capacity and quality of life are of immense importance but are not well understood. Aging- related behavioral change manifests vastly different patterns between individuals but little is known about the causes of individual differences in aging. It is generally agreed that the most powerful strategy to untangle genetic and environmental influences in the development of human characters is the adoption design, and that the most powerful adoption design is the study of twins reared apart (TRA). When coupled with longitudinal measurement, which is a necessary condition for directly assessing change, adoption designs provide a compelling basis for analyzing genetic and environmental etiologies of change as well as continuity in behavioral aging. Work already begun (SATSA project) with the elderly identified in the Swedish Twin registries represents an unprecedented opportunity to obtain longitudinal measurements on a large number of TRA. A proposed second and third wave of data collection will provide longitudinal measurements of cognitive, functional, personality, and health variables on 200 pairs of twins reared apart and 200 pairs of matched control twins reared together. Thus, the proposed project will extend an extent cross-sectional study of elderly twins in two important directions. One direction involves the incorporation of a longitudinal data collection perspective into the design. The second direction in which the project is being extended is the foci of the data analyses. In addition to the traditional behavioral genetic-based decomposition of the variance of markers into genetic and environmental sources, we will also apply more recently enunciated analysis models to the covariances among measures (e.g., behavioral and biological markers). This program of research will provide an unparalleled set of information for analysis. These findings should greatly enhance our understanding of the nature and etiologies of differential aging patterns.